In organizations that depend on portable devices to conduct operations, it is valuable to be able to know the battery condition of the batteries used to power the portable devices, in addition to the state of charge. An example of such an organization would be a public safety organization, such as police, fire, and rescue, and an example of portable devices would be the portable two-way radios used by such people in conducting operations. Public safety personnel going on a deployment need to have fully charged batteries that are in good condition. Accordingly, it is beneficial if the state of charge and battery condition are easily discernible before going on a deployment. The state of charge is akin to a fuel gauge, indicating approximately the proportion of battery capacity remaining in the battery. The condition of the battery is indicative of its age, in terms of both cycle life (the number of charge/discharge cycles) and chronological age, in addition to the random degradation over time. Typically as rechargeable batteries age their maximum capacity diminishes and their internal impedance increases.
Some manufacturers have built in so called “fuel gauges” into rechargeable battery packs that track, internally, charging and discharging, as well as charge/discharge cycles. The fuel gauge can retain state of charge and condition information in a memory in the rechargeable battery pack that can be read by a device powered by the battery pack. However, many battery packs do not have a fuel gauge capability.
Without the constant and close monitoring of battery current, both discharge and charge, it is difficult to determine the state of charge of a battery pack. The best way to determine the capacity of given battery pack and to charge it fully is to discharge it to an end of discharge condition, and then charge it to a fully charged condition, as indicated by certain known criteria based on battery parameters such as changes in voltage, temperature, and current while charging. Once a battery pack has been discharged and recharged then the capacity of the battery pack can be determined and it is then known that the battery pack is fully charged. However, determining capacity and state of charge does not directly indicate the condition of the battery—a fully charged battery near the end of its cycle life does not have the same capacity as new battery with very few charge/discharge cycles. Furthermore, discharging batteries can generate considerable heat, particular in organizations with a large number of batteries. This heat represents a loss of energy.
Accordingly, there is a need for an apparatus and method for discharging a battery to determine its condition, and further to make use of the energy dissipated from a battery upon being discharged.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.